JP2014016554A - Developing device and image forming apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To divide developer for two developer holding bodies, and stably hold and convey the resulting developer from the division toward respective development areas without giving excessive stress to the developer.SOLUTION: A developing device includes: a first developer holding body 2 that is arranged at a position opposite to an image holding body 1 and rotates in a direction opposite to a direction of rotation of the image holding body 1; a second developer holding body 3 that is arranged at a position opposite to the first developer holding body 2 and rotates in the same direction as the direction of rotation of the first developer holding body 2; a developer supply mechanism 4 that supplies developer G to either one of the first and second developer holding bodies 2 and 3; a developer division unit 6 that has division magnetic poles 7 (7a and 7b) having different polarities from each other arranged at opposing positions of the first and second developer holding bodies 2 and 3, and divides the developer G for the two developer holding bodies 2 and 3 in division magnetic fields formed by the division magnetic poles; and a developer conveying unit 9 that has conveyance magnetic poles 10 (10a and 10b) arranged respectively between development magnetic poles 8 (8a and 8b) and the respective division magnetic poles 7 of the first and second developer holding bodies 2 and 3, the conveyance magnetic poles 10 having polarity different from that of the magnetic poles 8 and 7, and holds and conveys the developer G after the division.

Description

  The present invention relates to a developing device and an image forming apparatus using the developing device.

Japanese Patent Application Laid-Open No. 2004-228561 provides a double-blade developer regulating member between adjacent developing rolls in an aspect having a pair of developing rolls facing the image carrier, and the developer regulating member and the magnetic poles of the developing rolls are mutually connected. A system is described in which a developer is supplied to each of both developing rolls by action.
Patent Document 2 has two developer holders arranged to face a latent image holder, and the developer supplied to one developer holder is held at two opposing portions by two developers. It is described that the delivery ratio for the two developer holding bodies is adjusted by changing the angle of the opposite polarity magnetic poles facing each other in the delivery section to be delivered to the body.
In Patent Document 3, in a mode having a pair of developing rolls facing the image bearing member, a doctor blade is disposed between the developing rolls, and the doctor blade is provided with a magnetic member and at a position facing the doctor blade. On the other hand, each developing roll is provided with a magnetic pole having a different polarity, and each developing roll has an opposing magnetic pole and a magnetic pole having a different polarity from the main pole between the opposing magnetic pole and the main pole (developing magnetic pole). Is described.
In Patent Document 4, in a mode having a pair of developing rolls facing the image carrier, a regulating member is provided between the developing rolls, and the developing rolls at positions facing each other across the regulating member have different polarities. In this configuration, only one developing roll is provided with a transport magnetic pole between the opposing magnetic pole and the main pole (developing magnetic pole).

Japanese Patent Laying-Open No. 2006-47840 (Example 1, FIG. 1) JP 2011-197289 A (Mode for carrying out the invention, FIG. 5) JP 2009-186614 A (Best Mode for Carrying Out the Invention, FIG. 1) JP 2007-47639 A (Example 1, FIG. 2)

  The problem to be solved by the present invention is to divide the developer supplied toward the opposite portions of the two developer holders without giving excessive stress to the developer. It is to stably hold and convey toward the developing area.

  The invention according to claim 1 is disposed to face the image holding body that holds and circulates the electrostatic latent image, and rotates in a direction opposite to the image holding body at a portion facing the image holding body and the image holding body. A first developer holder that holds and conveys a developer containing toner and a magnetic carrier toward a development area where the electrostatic latent image is developed, and holds an image from the first developer holder Is disposed opposite the image carrier and the first developer holder on the downstream side in the moving direction of the body, and is the same as the first developer holder at a portion facing the first developer holder. A second developer holder that rotates in the direction and holds and conveys the developer toward the development area where the electrostatic latent image on the image carrier is developed, and the first and second developer holders. The two developer retainers are located downstream of the development area in the rotation direction of the developer retainer with respect to any one of the members. A developer supply mechanism for supplying the developer to a position upstream from the opposite portion of the body, and the developer supplied by the developer supply mechanism for development in both the first and second developer holders. A dividing member formed by the dividing magnetic poles, which is provided with a regulating member for regulating the required amount, and dividing magnetic poles having different polarities from each other at the opposing portions of the first and second developer holders. A developer dividing unit that divides the developer supplied from the developer supply mechanism and transported to the opposing portion of the two developer holders into two developer holders; and the first and second developments Among the developer holders, a transporting magnetic pole having a different polarity from each other is disposed between the developing magnetic pole corresponding to each developing region and each of the dividing magnetic poles, and the magnetic flux density distribution of these transporting magnetic poles The magnetic flux density of the part adjacent to the developer dividing part is Is increased than when there is no transport magnetic pole is a developing apparatus is characterized by comprising: a developer conveying unit that holds conveyed toward the developing zone each in a state where the developer is separated after division.

According to a second aspect of the present invention, in the developing device according to the first aspect, the developer dividing unit is a developer holding body to which the developer is supplied by the developer supply mechanism among the dividing magnetic poles. The center position of the magnetic pole width along the circumferential direction of the split magnetic pole of the developer holder on the different side is in the circumferential direction of the split magnetic pole of the developer holder on the side to which the developer is supplied by the developer supply mechanism. The developing device is characterized in that the developing device is set so as to be shifted to the upstream side in the rotation direction of the developer holding body with respect to the center position of the magnetic pole width along.
According to a third aspect of the present invention, in the developing device according to the first or second aspect, the half-value width of the normal component of the magnetic flux density due to the dividing magnetic pole of each developer holder is θ1, and the magnetic flux density due to the conveying magnetic pole is A developing device characterized in that when the half-value width of the normal line component is θ2, both the dividing magnetic pole and the conveying magnetic pole in each developer holder satisfy the relationship θ1 <θ2. It is.
According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, the developer transport unit is a developer in which a developer is supplied by the developer supply mechanism among the transport magnetic poles. The central position of the magnetic pole width along the circumferential direction of the conveying magnetic pole on the developer holding body side on the side different from the developer holding body is for conveying the developer holding body on the side to which the developer is supplied by the developer supplying mechanism. The developing device is characterized in that the developing device is set so as to be deviated toward the upstream side in the rotation direction of the developer holding body with respect to the center position of the magnetic pole width along the circumferential direction of the magnetic pole.
According to a fifth aspect of the present invention, in the developing device according to any one of the first to fourth aspects, at least the developer holding body on the side to which the developer is supplied by the developer supply mechanism includes the developing magnetic pole, The developing device includes a split magnetic pole and the transport magnetic pole, and includes seven magnetic poles along a rotation direction of the developer holder.
According to a sixth aspect of the present invention, there is provided an image holding member that circulates and holds an electrostatic latent image, and the electrostatic latent image on the image holding member that is provided opposite to the image holding member by a developer. An image forming apparatus comprising: a developing device according to claim 1 for developing.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect of the present invention, the image forming apparatus is provided separately from the first and second developer holders, and is disposed to face the image carrier and One or a plurality of additional developer holders that hold and convey the developer toward the opposite development areas, and the developer that is held and conveyed by the first and second developer holders is further developed. An image forming apparatus comprising: a delivery unit that delivers to the agent holder.
The invention according to claim 8 is arranged to face the image holding body that holds and circulates the electrostatic latent image, and rotates in a direction opposite to the image holding body at a portion facing the image holding body and the image holding body. A first developer holder that holds and conveys a developer containing toner and a magnetic carrier toward a development area where the electrostatic latent image is developed, and holds an image from the first developer holder Is disposed opposite the image carrier and the first developer holder on the downstream side in the moving direction of the body, and is the same as the first developer holder at a portion facing the first developer holder. A second developer holder that rotates in the direction and holds and conveys the developer toward the development area where the electrostatic latent image on the image carrier is developed, and the first and second developer holders. The two developer retainers are located downstream of the development area in the rotation direction of the developer retainer with respect to any one of the members. A developer supply mechanism for supplying the developer to a position upstream from the opposite portion of the body, and the developer supplied by the developer supply mechanism for development in both the first and second developer holders. A dividing member formed by the dividing magnetic poles, which is provided with a regulating member for regulating the required amount, and dividing magnetic poles having different polarities from each other at the opposing portions of the first and second developer holders. A developer dividing unit that divides the developer supplied from the developer supply mechanism and transported to the opposing portion of the two developer holders into two developer holders; and the first and second developments Among the agent holders, the adjacent magnetic poles including the dividing magnetic pole and the developing magnetic pole are different in polarity from each other between the developing magnetic pole corresponding to each developing area and the dividing magnetic pole. Each of the above transfer magnetic poles is arranged, and these transfer magnetic poles Development that increases the magnetic flux density of the portion adjacent to the developer dividing portion by the magnetic flux density distribution as compared with the case where there is no magnetic pole for conveyance, and holds and conveys the divided developer toward each developing area in a separated state. And a developer transport unit.

According to the first aspect of the present invention, when dividing the developer supplied toward the opposing portions of the two developer holders, the divided developer is respectively applied without applying excessive stress to the developer. It is possible to provide a developing device capable of stably holding and transporting toward the developing area.
According to the second aspect of the present invention, it is possible to divide the developer into a predetermined division ratio for the two developer holders as compared with the case where this configuration is not provided.
According to the third aspect of the present invention, the magnetic flux density immediately after the division can be kept large compared to the aspect in which the magnetic pole width of the conveying magnetic pole is narrower than the magnetic pole width of the dividing magnetic pole.
According to the fourth aspect of the present invention, the developer divided into the two developer holders can be more stably held and conveyed toward the respective development areas as compared with the case where this configuration is not provided.
According to the invention of claim 5, by devising the magnetic pole configuration of the developer holding body, the developer supplied toward the opposed parts of the two developer holding bodies is divided, and the respective development zones are divided. It is possible to easily realize the behavior of the developer that stably holds and conveys the developer that has been divided toward the surface.
According to the invention of claim 6, when dividing the developer supplied toward the opposing portions of the two developer holders, the divided developers are respectively applied without applying excessive stress to the developer. It is possible to provide an image forming apparatus that can be stably held and conveyed toward the developing area.
According to the seventh aspect of the present invention, the development efficiency can be improved as compared with an embodiment in which there are two developer holders.
According to the eighth aspect of the invention, when dividing the developer supplied toward the opposing portions of the two developer holders, the divided developer is respectively applied without applying excessive stress to the developer. It is possible to provide a developing device capable of stably holding and transporting toward the developing area.

1 is a schematic diagram showing an outline of an embodiment of a developing device to which the present invention is applied. (A) shows the operation when only the split magnetic pole used in the developing device according to the comparative embodiment is provided, and (b) shows the operation when the split magnetic pole and the transport magnetic pole used in the developing device according to the embodiment are provided. It is explanatory drawing. 1 is a schematic diagram illustrating an overview of an image forming apparatus according to Embodiment 1. FIG. FIG. 2 is a schematic diagram illustrating an outline of a developing device according to the first embodiment. 3 is an explanatory diagram showing a magnetic pole arrangement according to Embodiment 1. FIG. FIG. 6 is an explanatory diagram illustrating a movement of a developer in the developing device according to the first embodiment. It is explanatory drawing which shows a magnetic pattern in case it does not have a magnetic pole for conveyance as a comparison form, (a) is a case where two developing rolls are separated to such an extent that it does not exert a magnetic action mutually, (b) is two This is a case where two developing rolls are close to each other so as to exert a magnetic action. FIG. 6 is an explanatory diagram showing a magnetic pattern when a conveyance magnetic pole is provided as in the first embodiment, where (a) is a case where two developing rolls are separated to such an extent that they do not exert a magnetic action on each other, and (b) Is the case where the two developing rolls are close to each other so as to exert a magnetic action. (A) is a schematic diagram showing a flow of a developer when a regulating member is provided between two developing rolls as a comparative form, and (b) is an explanatory diagram showing an example of the magnetic pattern. FIG. 4 is an explanatory diagram showing the action of the magnetic pole arrangement of the dividing magnetic poles, in which (a) shows that the dividing magnetic poles of the first developing roll are biased upstream from the dividing magnetic poles of the second developing roll as in the first embodiment. When arranged, (b) is arranged at the position where the dividing magnetic poles of the first developing roll and the second developing roll are opposed to each other, and (c) is the dividing magnetic pole and the conveying magnetic pole of the first developing roll being the first. The case where it arrange | positions in the downstream from the magnetic pole for a division | segmentation of a 2 image development roll is shown is shown. It is explanatory drawing which shows the effect | action by the magnitude | size of the magnetic pole width (half value width) of a division | segmentation magnetic pole and a conveyance magnetic pole, (a) is the case where the conveyance magnetic pole is larger than the division | segmentation magnetic pole, (b) is the conveyance magnetic pole This is a case where the direction is smaller than the dividing magnetic pole. It is explanatory drawing which shows an effect | action at the time of changing the position of the magnetic pole for conveyance, and shows the case where the magnetic pole for conveyance is arrange | positioned in the position of (b) nearer to the magnetic pole for division than (a). FIG. 10 is an explanatory diagram illustrating the movement of a developer in the developing device according to the second embodiment. FIG. 10 is a schematic diagram illustrating an outline of a developing device according to a third embodiment. FIG. 10 is an explanatory diagram illustrating the movement of a developer in the developing device according to the third embodiment. FIG. 10 is an explanatory diagram showing the movement of a developer in the developing device according to Embodiment 4. FIG. 10 is a schematic diagram illustrating an outline of a developing device according to a fifth embodiment. FIG. 10 is an explanatory diagram illustrating the movement of a developer in the developing device according to the fifth embodiment. FIG. 6 is an explanatory diagram illustrating an example of a magnetic pattern when the seven-pole developing rolls of Example 1 are arranged to face each other. It is explanatory drawing which shows the example of a magnetic pattern when the developing roll of 5 pole structure is arrange | positioned facing as a comparative example. FIG. 10 is an explanatory diagram showing the arrangement of evaluation models in Example 2. It is a graph which shows the result of Example 2, and shows the case where the half value width of the magnetic pole for conveyance is 30 degrees. It is a graph which shows the result of Example 2, and shows the case where the half value width of the magnetic pole for conveyance is 20 degrees.

Outline of Embodiment First, an outline of an embodiment of a developing device to which the present invention is applied will be described.
FIG. 1 is a schematic diagram showing an outline of a developing device according to an embodiment model embodying the present invention. The developing device is disposed opposite to the image carrier 1 that holds the electrostatic latent image and circulates and rotates in a direction opposite to the image carrier 1 at a portion facing the image carrier 1 and the image carrier. A first developer holding body 2 that holds and conveys a developer G containing toner and a magnetic carrier toward a developing area Da in which the electrostatic latent image on 1 is developed; and the first developer holding The image carrier 1 is disposed on the downstream side of the image carrier 1 in the moving direction of the image carrier 1 so as to face the image carrier 1 and the first developer carrier 2, and the first developer carrier 2 is opposed to the first developer carrier 2. A second developer holder 3 that rotates in the same direction as the developer holder 2 and holds and conveys the developer G toward the development area Db where the electrostatic latent image on the image holder 1 is developed; , One of the first and second developer holders 2 and 3 on the downstream side of the developing area Db in the rotation direction of the developer holder 3. The developer supply mechanism 4 that supplies the developer G to a position upstream of the opposed portions of the two developer holders 2 and 3, and the developer G supplied by the developer supply mechanism 4 is the first and second developer G. The regulating member 5 that regulates the amount required for development by both of the two developer holders 2 and 3 and the division of the first and second developer holders 2 and 3 opposite in polarity to each other The magnetic poles 7 (7a, 7b) are arranged, supplied from the developer supply mechanism 4 by the dividing magnetic field formed by these dividing magnetic poles 7, and conveyed to the opposite portions of the two developer holders 2 and 3 Corresponding to the development areas Da and Db of the developer dividing section 6 that divides the developed developer G into two developer holding bodies 2 and 3 and the first and second developer holding bodies 2 and 3 Between the developing magnetic pole 8 (8a, 8b) and the respective dividing magnetic poles 7 to be conveyed, (10a, 10b) are arranged respectively, and the magnetic flux density distribution of these conveying magnetic poles 10 increases the magnetic flux density of the portion adjacent to the developer dividing portion 6 as compared with the case where there is no conveying magnetic pole 10, thereby developing after dividing. And a developer transport unit 9 that holds and transports the developer G toward the developing areas Da and Db in a state where the agent G is separated.

  Here, the first and second developer holders 2 and 3 may be any one that can hold and convey a developer (two-component developer) G containing toner and a magnetic carrier on its peripheral surface. The peripheral surfaces of the agent holders 2 and 3 are subjected to processing such as grooving and roughening so that the developer G is conveyed. A typical embodiment of such developer holders 2 and 3 includes a magnet body having a non-magnetic cylindrical rotating body on the surface and a permanent magnet fixedly disposed therein. .

  Further, the developer supply mechanism 4 only has to supply the developer G to one of the first and second developer holders 2 and 3. In this example, the developer supply mechanism 4 is disposed on the second developer holder 3 side. Although the aspect which supplies the developer G was shown, it is not restricted to this, You may supply the developer G to the 1st developer holding body 2 side. Further, the regulating member 5 regulates a necessary amount of the developer G to be conveyed to the opposed portion of the two developer holding bodies 2 and 3, and is provided to face the developer holding body 3. Alternatively, the developer G before being supplied to the developer holding body 3 may be regulated.

  The developer dividing unit 6 transfers the developer G transported to the opposite part of the two developer holders 2 and 3 by one developer holder 3 to each of the first and second developer holders 2 and 3. And is divided by a dividing magnetic field formed by dividing magnetic poles 7 (7a, 7b) having different polarities. By providing such a developer dividing section 6, no member is disposed at the opposing portion of the two developer holding bodies 2, 3, so that excessive stress is not applied to the developer G. Further, since the developer G is divided by the dividing magnetic pole 7, even if the amount of the developer is increased or decreased, the developer G is divided with a stable division ratio. The arrangement of the dividing magnetic poles 7 (7a, 7b) may be arranged corresponding to the closest part of the two developer holders 2 and 3, or within the range where the dividing magnetic field acts. However, they may be arranged so as to be biased with respect to each other.

  The developer transport unit 9 transports the developer G divided into the two developer holders 2 and 3 by the developer dividing unit 6 toward the developing areas Da and Db. By such a magnetic flux density distribution of the conveying magnetic pole 10, the magnetic flux density in a portion adjacent to the developer dividing portion 6 is increased, and the magnitude of the magnetic flux density of the conveying magnetic pole 10 is divided by the developer dividing portion 6. The separated developer G is set to a size to be conveyed in a separated state, and the divided developer G is received between the two developer holders 2 and 3 by the magnetic field generated by the divided conveyance magnetic pole 10. It is not passed.

Here, the flow of the developer G when the developer dividing unit 6 and the developer transport unit 9 are provided will be described.
FIG. 2 (a) shows, as a comparative form, a mode in which each developer holder 2 and 3 includes only the developer dividing section 6 including the split magnetic poles 7 (7a and 7b) and does not include the developer transport section 9. FIG. 6B is an explanatory diagram showing the flow of the developer G, and (b) is a mode in which each developer holding body 2, 3 includes a developer dividing section 6 and a developer transport section 9 as in the present embodiment. FIG. 6 is an explanatory diagram showing the flow of developer G.

  Now, as shown in FIG. 2A, in the embodiment in which the first and second developer holders 2 and 3 include only the developer dividing section 6, the flow of the developer G is estimated as follows. The developer G supplied to the opposite portions of the two developer holders 2 and 3 is divided into two developer holders 2 and 3 by the developer dividing section 6 composed of split magnetic poles 7a and 7b having different polarities. . Here, since neither developer holding body 2 or 3 has a magnetic pole between the magnetic poles 7a and 7b for division and the magnetic poles 8a and 8b for development located in the development areas Da and Db, the magnetic pole for division. The developer G spiked by 7a, 7b has a very small force received from the developer holders 2, 3 between the split magnetic poles 7a, 7b and the developing magnetic poles 8a, 8b. At this time, since the distance from the magnetic poles 7a and 7b for division to the magnetic poles 8a and 8b for development is long, the divided developer G is not bound by the developer holders 2 and 3, and the developer is peeled off. Become. For this reason, the flow of the developer G after division is difficult to stabilize, and the developer G on the developer holding bodies 2 and 3 after division is likely to contact each other. It becomes difficult to maintain the developer amount by the ratio. Further, the variation in the layer thickness of the developer G reaching the developing magnetic poles 8a and 8b also becomes large, and for example, image unevenness may occur during development.

  On the other hand, as shown in FIG. 2B, in the embodiment in which the first and second developer holders 2 and 3 include the developer dividing unit 6 and the developer transporting unit 9, the flow of the developer G is as follows. Is estimated. In each developer holding body 2 and 3, the developer dividing section 6 composed of the split magnetic poles 7a and 7b and the developer transport section 9 composed of the transport magnetic poles 10a and 10b are arranged close to each other. A sufficient magnetic flux density is ensured between the split magnetic poles 7a and 7b and the transport magnetic poles 10a and 10b in the developer holders 2 and 3. Therefore, the separated developer G is prevented from being peeled off from the developer holders 2 and 3, and the developer is sufficiently bound by the developer holders 2 and 3. Thereby, the mutual contact of the developer G on the developer holding bodies 2 and 3 after the division is also suppressed, and the developer G in which the developer amount having a stable division ratio is maintained in the developer G after the division, respectively. Are conveyed toward the developing areas Da and Db. Further, the developer G transported toward the development areas Da and Db in this way can be prevented from being separated from the respective developer holders 2 and 3, and the variation in the layer thickness of the developer G can be suppressed. The occurrence of image unevenness during development is also suppressed.

  Further, in FIG. 1, from the viewpoint of dividing the developer G by the developer dividing unit 6 at a predetermined division ratio, the developer dividing unit 6 includes the developer supply mechanism 4 among the dividing magnetic poles 7a and 7b. The central position of the magnetic pole width along the circumferential direction of the split magnetic pole 7a of the developer holder 2 on the side different from the developer holder 3 to which the developer G is supplied at the developer supply mechanism 4 is the developer. G is set so as to be shifted to the upstream side in the rotation direction of the developer holding body 2 with respect to the center position of the magnetic pole width along the circumferential direction of the dividing magnetic pole 7b of the developer holding body 3 on the side to which G is supplied. It is preferable that In this way, by biasing one of the split magnetic poles 7a to the upstream side relative to the other, the developer conveying force of the developer G that has been conveyed on the developer holding body 3 toward the opposite portion is resisted. In addition, by exerting an action of sucking the developer G toward the developer holding body 2 side, and further exerting an action of returning a part of the developer G sucked in a large amount thereafter, a predetermined division ratio is obtained. Thus, the developer G is divided. At this time, by making the peak values of the normal component of the magnetic flux density in the two split magnetic poles 7a and 7b substantially the same, the split ratio can be easily divided equally. If the peak value of the normal component of the magnetic flux density in the two split magnetic poles 7a and 7b is changed, the split ratio changes according to the peak value. Details will be described later.

  Further, from the viewpoint of further stabilizing the flow of the developer G divided by the developer dividing unit 6, the half-value width of the normal component of the magnetic flux density by the dividing magnetic pole 7 of each developer holder 2, 3 is set to θ1. When the half-value width of the normal component of the magnetic flux density by the transport magnetic pole 10 is θ2, the dividing magnetic pole 7 and the transport magnetic pole 10 in each developer holder 2 and 3 both satisfy the relationship θ1 <θ2. It is preferable that it is set to. In this way, by making the half width of the conveying magnetic pole 10 larger than the half width of the dividing magnetic pole 7, the magnetic flux density acting on the developer G immediately after the division is increased, and the developer holding of the developer G immediately after the division is held. Peeling from the bodies 2 and 3 is further suppressed. Details will be described later.

  Further, from the viewpoint of further suppressing the separation of the developer G from the developer holders 2 and 3 when the developer G is transported by the developer transport unit 9, the developer transport unit 9 includes the transport magnetic pole 10. Among them, the central position of the magnetic pole width along the circumferential direction of the conveying magnetic pole 10a on the side of the developer holding body 2 on the side different from the developer holding body 3 to which the developer G is supplied by the developer supply mechanism 4 is developed. With respect to the center position of the magnetic pole width along the circumferential direction of the conveying magnetic pole 10b of the developer holding body 3 on the side to which the developer G is supplied by the developer supplying mechanism 4, the upstream side in the rotation direction of the developer holding body 2. It is preferable to set the position to be biased. The transport magnetic poles 10a and 10b are arranged in a biased manner to further prevent the developer G divided into the developer holding body 2 on the side where the developer G is not supplied from being separated from the developer holding body 2. As a result, the conveyance of the developer G becomes more stable. In such a bias arrangement, the split magnetic pole 7a and the transport magnetic pole 10a of the developer holder 2 on the side to which the developer G is not supplied are both biased and arranged upstream. Is preferred.

  Further, from the viewpoint of improving the transportability of the developer G while simplifying the configuration of the developer holders 2 and 3, at least the developer holding side on which the developer G is supplied by the developer supply mechanism 4. The body 3 includes a developing magnetic pole 8b, a dividing magnetic pole 7b, and a conveying magnetic pole 10b, and preferably includes seven magnetic poles along the rotation direction of the developer holder 3. By providing seven magnetic poles, it becomes possible to give the function of regulation, division, conveyance, development, conveyance, and peeling from the suction of the developer G to one developer holding body 3. The operation from the attachment to the separation of the developer G is effectively performed by the developer holder 3.

  In order to apply such a developing device to an image forming apparatus, an image holding body 1 that holds and circulates an electrostatic latent image, and an image holding body 1 that is provided so as to face the image holding body 1. The developing device described above may be used as a developing device for developing the upper electrostatic latent image with the developer G. Such an image carrier 1 may be not only a drum shape but also a belt shape.

  Further, the image forming apparatus is not limited to the aspect including the first and second developer holders 2 and 3, and the first and second developer holders 2 and 2 are provided for one image holder 1. In addition to 3, an additional developer holding member may be applied. Examples of such an aspect include the following aspects. That is, provided separately from the first and second developer holders 2 and 3, the developer G is arranged facing the image carrier 1 and holding the developer G toward the development area facing the image carrier 1. And one or a plurality of additional developer holders to be conveyed, and a delivery unit for delivering the developer G held and conveyed by the first and second developer holders 2 and 3 to the additional developer holder. Suffices to be provided.

  Here, the additional developer holder may be arranged on one side of the first and second developer holders 2 and 3 or on both sides. Further, an additional developer holding body may be provided on the upstream side or downstream side of the additional developer holding body via a delivery unit.

  And as the developer conveyance part 9, it is also possible to equip each developer holding body 2 and 3 with the some magnetic pole 10 for conveyance, In this case, what is necessary is just as follows as a developing device. That is, it is arranged opposite to the image carrier 1 that holds the electrostatic latent image and circulates and rotates in a direction opposite to the image carrier 1 at a portion facing the image carrier 1 and on the image carrier 1. From a first developer holding body 2 that holds and conveys a developer G containing toner and a magnetic carrier toward the development area Da where the electrostatic latent image is developed, and from the first developer holding body 2 The first developer holding member is disposed opposite to the image holding member 1 and the first developer holding member 2 on the downstream side in the moving direction of the image holding member 1, and is opposed to the first developer holding member 2. A second developer holding body 3 which rotates in the same direction as the body 2 and holds and conveys the developer G toward the developing area Db where the electrostatic latent image on the image holding body 1 is developed; And any one of the second developer holders 2 and 3 downstream of the development zone Db in the rotation direction of the developer holder 3 and A developer supply mechanism 4 for supplying the developer G to a position upstream of the opposed portions of the two developer holders 2 and 3, and the developer G supplied by the developer supply mechanism 4 as first and second A regulating member 5 that regulates the amount required for development on both the developer holders 2 and 3, and split magnetic poles having different polarities at opposite portions of the first and second developer holders 2 and 3 7 is arranged, and the developer G supplied from the developer supply mechanism 4 by the dividing magnetic field formed by these dividing magnetic poles 7 and transported to the opposing portion of the two developer holders 2 and 3 is supplied to the developer G. The developer dividing section 6 that divides the developer holders 2 and 3 and the developing magnetic poles 8 corresponding to the development areas Da and Db of the first and second developer holders 2 and 3, respectively. The adjacent magnetic poles including the dividing magnetic pole 7 and the developing magnetic pole 8 are different in polarity from each other. One or more transporting magnetic poles 10 are arranged as described above, and the magnetic flux density distribution of these transporting magnetic poles 10 increases the magnetic flux density in the portion adjacent to the developer dividing section 6 as compared with the case where there is no transporting magnetic pole 10. In addition, a developer transport unit 9 that holds and transports the divided developer G toward the development areas Da and Db in a separated state may be provided. In such an embodiment, the number of the magnetic poles 10 for conveyance is not limited, and a plurality of developer holders 2 and 3 may be provided, or one may be provided and the other may be provided. .

Next, the present invention will be described in more detail based on embodiments shown in the drawings.
Embodiment 1
FIG. 3 is a schematic diagram showing an outline of the image forming apparatus according to the first embodiment in which the developing device to which the present invention is applied is used. In the figure, the image forming apparatus according to the present embodiment employs, for example, an electrophotographic system, and a four-color developer in which toner and a magnetic carrier are included in a substantially linear portion of the intermediate transfer belt 30 that circulates and rotates. The image forming devices 20 (20a to 20d) that perform image formation using (two-component developer) are arranged side by side.

<Overall configuration of image forming apparatus>
Since each image forming device 20 (specifically, 20a to 20d) has substantially the same configuration, one image forming device 20a will be described as a representative image forming device 20 here. The image forming apparatus 20 develops an electrostatic latent image on the photosensitive member 21 with a developer provided as opposed to the photosensitive member 21 as an image holding member that rotates while holding the electrostatic latent image. The developing device 40 is provided. Further, around the photosensitive member 21, a charger 22 for charging the photosensitive layer of the photosensitive member 21 to a predetermined potential, and a latent image based on an image signal on the photosensitive member 21 charged by the charger 22. The exposure device 23 is exposed so that a latent image is formed, and the latent image formed by the exposure by the exposure device 23 is developed with a developer and visualized by the developing device 40 and the developing device 40. A primary transfer roll 24 that transfers the toner image onto the intermediate transfer belt 30, a cleaner 25 that cleans the residue on the photoreceptor 21 after the toner image is transferred, and the like are provided.

  Here, although the aspect of the corona charger is shown as the charger 22, it is not limited thereto, and for example, a contact-type charging method may be adopted. Moreover, although the LED array type | mold aspect is shown as the exposure device 23, you may employ | adopt a laser scanning type | mold, for example. Further, although the primary transfer roll 24 is shown in contact with the intermediate transfer belt 30, for example, a system in which the primary transfer roll 24 is separated from the intermediate transfer belt 30 using a corona charger may be adopted.

  The intermediate transfer belt 30 is stretched around a plurality of stretching rolls 31 to 33, and circulates and rotates using, for example, the stretching roll 31 as a driving roll. Further, a secondary transfer roll 34 is disposed at a position facing the tension roll 33 across the intermediate transfer belt 30, and the tension roll 33 is used as a backup roll between the secondary transfer roll 34 and the backup roll 33. By applying a secondary transfer electric field to the toner image, the toner image on the intermediate transfer belt 30 is transferred onto the recording material P. Reference numeral 35 in the drawing is a belt cleaner for cleaning residual toner on the intermediate transfer belt 30. In this example, the intermediate transfer belt 30 is used. However, for example, a drum-shaped intermediate transfer member may be used instead of the intermediate transfer belt 30. Further, instead of the intermediate transfer belt 30, a recording material conveying belt that holds and conveys the recording material is used, and the toner images by the image forming device 20 are sequentially transferred onto the recording material held on the recording material conveying belt. You may do it.

  In the present embodiment, the recording material P is supplied to the secondary transfer site, and a conveyance path for the recording material P is provided from the secondary transfer site until the recording material P is discharged. Such a member is provided. At a position adjacent to the upstream side of the secondary transfer portion in the conveyance direction of the recording material P, the recording material P toward the secondary transfer portion is positioned, and the positioned recording material P is secondary at a predetermined timing. A registration roll 36 is provided for transporting toward the transfer site. Further, on the downstream side of the secondary transfer portion, a conveyance belt 37 that conveys the recording material P on which the toner image has been transferred at the secondary transfer portion, and an unfixed toner image on the recording material P on the downstream side of the conveyance belt 37. And a discharge roller 39 for discharging the recording material P on which the unfixed toner image is fixed by the fixing unit 38 to the outside of the apparatus.

<Configuration of developing device>
The developing device 40 of the present embodiment is configured as shown in FIG. The developing device 40 is provided with two developer holders arranged to face the photosensitive member 21 corresponding to the opening of the developing container 41. These developer holders are a first developing roll 42A as a first developer holding body and a second developing roll 42B as a second developer holding body. The first developing roll 42A rotates in the opposite direction to the photosensitive member 21 at a portion facing the photosensitive member 21, and holds and conveys the developer containing toner and magnetic carrier toward the developing area DA. On the other hand, the second developing roll 42B is disposed downstream of the first developing roll 42A in the rotation direction of the photoconductor 21, and rotates in the same direction as the photoconductor 21 at a portion facing the photoconductor 21. The developer is held and conveyed toward the area DB.

  The first developing roll 42A has a developing sleeve 43A (non-magnetic cylindrical rotating body) that conveys the developer while holding the developer on its peripheral surface, and a fixed magnetic pole arrangement that is fixedly provided in the developing sleeve 43A. And a magnet body 44A on which magnets are arranged. Similarly to the first developing roll 42A, the second developing roll 42B is also provided with a developing sleeve 43B that holds and conveys the developer on the peripheral surface thereof, and a fixed magnetic pole arrangement that is fixedly provided in the developing sleeve 43B and predetermined. And a magnet body 44B on which magnets are arranged. For example, V-shaped grooves extending along the width direction intersecting the rotation direction are formed on the peripheral surfaces of the developing sleeves 43A and 43B at predetermined intervals along the rotation direction.

  The magnetic poles in the magnet bodies 44A and 44B are arranged so that the developer is sufficiently transported. In this example, both of the magnet bodies 44A and 44B have seven magnetic poles inside along the rotation direction. A magnetic pole is arranged. The magnet body 44A of the first developing roll 42A is, from the N1 pole as the developing magnetic pole 62 corresponding to the developing area DA, in the order of the S1 pole, N2 pole, S2 pole, along the rotation direction of the first developing roll 42A. S3 pole, N3 pole, and S4 pole are arranged. Here, the S1 pole and the N2 pole are magnetic poles for transporting the developer, and the S2 pole is a magnetic pole for peeling the developer from the first developing roll 42A, and the S3 pole of the same polarity adjacent to the downstream side. The developer is peeled from the first developing roll 42A by the repulsive magnetic field between the two. The N3 pole is a dividing magnetic pole 61 constituting the developer dividing portion, and the S4 pole is a conveying magnetic pole 63 constituting the developer conveying portion.

  On the other hand, in the magnet body 44B of the second developing roll 42B, the S1 pole as the developing magnetic pole 62 is disposed at a position corresponding to the developing area DB, and the N1 pole in order along the rotation direction of the second developing roll 42B. S2 pole, S3 pole, N2 pole, S4 pole, and N3 pole are arranged. Here, the N1 pole is a magnetic pole for transporting the developer, and the S2 pole is a magnetic pole for peeling the developer from the second developing roll 42B, between the S3 pole of the same polarity adjacent to the downstream side. The developer is peeled from the second developing roll 42B by the repulsive magnetic field. The S3 pole is also a magnetic pole for attracting the developer to the second developing roll 42B, and the developer is supplied to the second developing roll 42B by the attracting action of the S3 pole. Further, the N2 pole is a regulating magnetic pole disposed with respect to a regulating member 45 (described later) that regulates the layer thickness of the developer supplied to the second developing roll 42B. Further, the S4 pole is a dividing magnetic pole 61 constituting the developer dividing portion, and the N3 pole is a conveying magnetic pole 63 constituting the developer conveying portion. The arrangement of the magnetic poles in the first developing roll 42A and the second developing roll 42B is not limited to the above-described embodiment, and may be appropriately selected within a range that does not hinder the developer flow.

The split magnetic pole 61 and the transport magnetic pole 63 of this embodiment are arranged as shown in FIG. That is, in the first developing roll 42A, an angle formed by a line segment connecting the central axis OA and the circumferential center of the dividing magnetic pole 61 and a line segment connecting the central axis OA and the circumferential center of the conveying magnetic pole 63. On the other hand, in the second developing roll 42B, a line connecting the central axis OB and the circumferential center of the dividing magnetic pole 61 and a line connecting the central axis OB and the circumferential center of the conveying magnetic pole 63 are The angle between the minutes is β. That is, the dividing magnetic pole 61 of the first developing roll 42A is upstream in the rotational direction of the first developing roll 42A from the line connecting the central axis OA of the first developing roll 42A and the central axis OB of the second developing roll 42B. Are offset by an angle α.
Here, in order to make the first developing roll 42A and the second developing roll 42B of the present embodiment easy to understand, the line segment connecting the center axes OA and OB is directed in the vertical direction. As shown in FIG. 4, they are arranged with an inclination of about 7 ° (the first developing roll 42A is inclined to the photosensitive member 21 side). In the figure, reference sign g1 denotes a gap between the first developing roll 42A and the second developing roll 42B. In FIG. 5, the split magnetic pole 61 (S4) is located on the line connecting the central axes OA and OB, but it is needless to say that the present invention is not limited to this.

  Furthermore, the first developing roll 42A and the second developing roll 42B are connected to power supplies 56A and 56B, respectively, for supplying a voltage in which an AC electric field is superimposed on a DC electric field, for example, a grounded photoconductor. A developing electric field is applied between the developing roller 21 and the developing rolls 42A and 42B.

  Two resin blocks 47a and 47b supported by the developing container 41 are disposed behind the first developing roll 42A and the second developing roll 42B in the developing container 41. A restriction member 45 is attached to these resin blocks 47a and 47b, and the layer thickness of the developer on the second developing roll 42B is restricted between the N2 pole as the restricting magnetic pole of the second developing roll 42B. It has become. The regulating member 45 of the present embodiment is arranged on the side close to the N2 pole of the second developing roll 42B and made of a magnetic material, and the downstream side in the rotational direction of the second developing roll 42B from the regulating piece 45a. And a regulating plate 45b made of a nonmagnetic material that is arranged adjacent to the regulating piece 45a and is thicker than the regulating piece 45a. A guide member 46 that guides the developer peeled off from the first developing roll 42A downward is provided obliquely above the resin block 47a.

  Further, in the developing container 41, behind the second developing roll 42B, a developer stirring mechanism is provided for conveying the developer while stirring and supplying the stirred developer to the second developing roll 42B. ing. The developer agitating mechanism includes two developer transport paths 51 extending substantially in parallel with a partition wall 41a (consisting of a part of the developing container 41) extending along the axial direction of the first and second developing rolls 42A and 42B. , 52 are provided in the developer transport paths 51, 52, respectively, with stirring and transporting members 53, 54 for transporting the developer while stirring the spiral blades. Further, on both end sides of the partition wall 41a in the axial direction of the agitating and conveying members 53 and 54, passages (not shown) connecting the two developer conveying paths 51 and 52 are formed, and the developer passes through these paths. Through the two developer transport paths 51 and 52. In the present embodiment, of the two agitating / conveying members 53 and 54, the agitating / conveying member 53 on the side close to the second developing roll 42B is a member that mainly supplies the developer to the second developing roll 42B. The agitating and conveying member 54 is a member that mainly agitates the developer and charges it to a desired charge amount.

  Further, a hole is formed in a part of the developer container 41 at an obliquely lower portion of the developer transport path 52 on the side far from the second developing roll 42B, and a change in magnetic permeability is detected corresponding to this hole. Thus, a magnetic permeability type concentration sensor 55 for detecting the toner concentration in the developer is attached. Needless to say, for example, the developer transport path 52 is replenished with toner using a replenishment mechanism (not shown) or with developer mixed with toner and magnetic carrier.

  In the present embodiment, in particular, the developer division that divides the developer on the second developing roll 42B regulated by the regulating member 45 into the developing rolls 42A and 42B at the opposing portions of the two developing rolls 42A and 42B. And a developer transport unit that transports the developer divided by the developer dividing unit toward the development areas DA and DB. More specifically, the first developing roll 42A and the second developing roll 42B are divided into magnetic poles 61 having different polarities (corresponding to the N3 pole of the first developing roll 42A and the S4 pole of the second developing roll 42B), and for the splitting. A conveying magnetic pole 63 (S4 pole of the first developing roll 42A and N3 of the second developing roll 42B) provided downstream of the magnetic pole 61 in the rotation direction of the developing rolls 42A and 42B and having a different polarity from the respective dividing polarities 61. The pole is equivalent).

  In addition, the magnetic flux densities of the dividing magnetic pole and the conveying magnetic pole are set as follows. Dividing magnetic pole 61 (corresponding to N3 pole of first developing roll 42A and S4 pole of second developing roll 42B) and conveying magnetic pole 63 (S4 pole of first developing roll 42A and N3 pole of second developing roll 42B) The peak value of the normal component of the magnetic flux density of the developing roll alone is smaller than the magnetic pole for conveyance 61 than the magnetic pole for conveyance 63, and when the two development rolls are arranged to face each other, the magnetic pole for conveyance is 63 is made smaller than the dividing magnetic pole 61. Further, between the S4 pole of the first developing roll 42A as the conveying magnetic pole 63 and the N3 pole of the second developing roll 42B, the peak value of the normal component of the magnetic flux density of these magnetic poles does not pass the developer. The size is not. Note that the peak values of the normal components of the magnetic flux densities of the first and second developing rolls 42A and 42B between the split magnetic poles 61 and the transport magnetic poles 63 are substantially equal.

<Operation of Image Forming Apparatus>
As shown in FIG. 3, the image forming apparatus according to the present embodiment has a primary transfer in which toner images formed on the respective photoreceptors 21 of the four image forming apparatuses 20 are opposed to the primary transfer roll 24. The toner images are sequentially transferred onto the intermediate transfer belt 30 at the portion, and a multiplexed toner image is formed on the intermediate transfer belt 30. The multiplexed toner image multiplexed on the intermediate transfer belt 30 is placed on the recording material P supplied from a recording material supply unit (not shown) at the secondary transfer portion that is the portion facing the secondary transfer roll 34. Secondary transferred. The recording material P onto which the toner image has been transferred is conveyed to a fixing device 38 via a conveying belt 37, fixed by the fixing device 38, and then discharged from a discharge roll 39 to, for example, a recording material container outside the apparatus.

<Operation of developing device>
FIG. 6 is an explanatory view showing the movement of the developer G around the first developing roll 42A and the second developing roll 42B, and the operation in the developing device 40 will be described with reference to this figure.
The developer G supplied onto the second developing roll 42B by the suction action of the S3 pole of the second developing roll 42B is sufficiently spiked between the N2 pole as the regulating magnetic pole and the regulating member 45, and is regulated. The layer thickness of the developer G is regulated by the gap at the closest portion between the member 45 and the second developing roll 42B. The developer G on the second developing roll 42B regulated by the regulating member 45 has two magnetic poles, that is, the S4 pole as the dividing magnetic pole 61 on the second developing roll 42B side and the division on the first developing roll 42A side. Part of the second developing roll 42A is moved from the second developing roll 42B side to the first developing roll 42A side by the attraction action by the normal component of the magnetic flux density between the N3 pole as the magnetic pole 61 and the rest is the second developing roll. Divided into 42B. Therefore, the divided developing agents G are held on the developing rolls 42A and 42B, respectively. Hereinafter, for the sake of clarity, the developer on the first developing roll 42A after the division is represented as G1, and the developer on the second development roll 42B after the division is represented as G2.

  In this embodiment, the N3 pole of the first developing roll 42A as the split magnetic pole 61 and the S4 pole of the second developing roll 42B, and the N1 pole and the second of the first developing roll 42A as the developing magnetic pole 62 are used. Since the S4 pole and the N3 pole are provided as the conveying magnetic pole 63 between the S1 pole of the developing roll 42B, as shown in FIG. 2, the divided developers G1 and G2 are supplied to the developing roll 42A. , 42 </ b> B is suppressed from being peeled off and conveyed to the developing areas DA and DB as they are. Therefore, the divided developers G1 and G2 maintain the developer amount corresponding to the dividing ratio in the developer dividing section and have a small variation in the layer thickness in the respective developing areas DA and DB. It is conveyed toward.

-About the developer dividing action of the developing device according to the comparative form-
First, a magnetic pattern in a case where the conveyance magnetic pole 63 is not provided as a comparative form, that is, an aspect in which the division magnetic pole 61 and the development magnetic pole 62 are arranged adjacent to each other will be described. It is assumed that the normal components of the magnetic flux densities of the dividing magnetic pole 61, the developing magnetic pole 62, and the conveying magnetic pole 63 in the two developing rolls 42A and 42B are the same.

  FIG. 7A shows an example of a magnetic pattern in a state where the two developing rolls 42A ′ and 42B ′ are separated by a distance (corresponding to g0 in the drawing) where the magnetic action of the two developing rolls 42A ′ and 42B ′ is not present when there is no magnetic pole 63 for conveyance. Is shown. Each of the developing rolls 42A ′ and 42B ′ has a similar magnetic pattern, and a normal component Ra of the magnetic flux density by the dividing magnetic pole 61 and a normal component Rb of the magnetic flux density by the developing magnetic pole 62 are used. The peak value of the tangential component Ta of the magnetic flux density appears at approximately the center of the two magnetic poles (the split magnetic pole 61 and the developing magnetic pole 62).

  In order to arrange the two developing rolls 42A ′ and 42B ′ facing each other and to divide the developer using only the split magnetic poles 61 having different polarities, the two developing rolls 42A ′ and 42B ′ are brought close to each other. It needs to be placed in position and have sufficient magnetic action. When the developing rolls 42A ′ and 42B ′ are brought close to the extent that the developer is divided by the magnetic action of the dividing magnetic pole 61 (corresponding to g1 in the figure: g1 << g0), as shown in FIG. Occurs. That is, when the splitting magnetic poles 61 of different polarities are arranged close to each other, the normal component Ra ′ of the magnetic flux density by the splitting magnetic pole 61 has a peak value larger than the normal component Ra of (a). Become. As a result, the tangential component Ta ′ of the magnetic flux density changes from the tangential component Ta of (a), and the peak value moves to the developing magnetic pole 62 side. Therefore, among the tangential components Ta ′, the size of the portion (the portion indicated by Q in the drawing) in which the normal components (Ra, Ra ′) of the dividing magnetic pole 61 have started to be reduced is (b) ( smaller than a). In (b), the Q portion on the developing roll 42B 'side is omitted.

  Thus, if the tangential component of the magnetic flux density is small in the region where the magnetic flux density in the normal direction is small between the split magnetic pole 61 and the developing magnetic pole 62, the developer divided by the split magnetic pole 61 is as shown in FIG. 2, since the binding force to the developing rolls 42A ′ and 42B ′ is small, the developing rolls 42A ′ and 42B ′ are easily peeled off. As described above, when the developer is divided only by the magnetic action of the dividing magnetic pole 61 at the divided portion (corresponding to the developer dividing portion), the two developing rolls 42A ′ and 42B ′ have to be arranged close to each other. For this reason, the transport force acting on the developer after the division becomes small, and the transport of the developer becomes unstable.

-About the dividing action of the developer of the developing device according to the embodiment-
On the other hand, it is advantageous to provide a conveying magnetic pole 63 that increases the conveying force of the developer between the dividing magnetic pole 61 and the developing magnetic pole 62 as in the present embodiment. FIG. 8 shows a magnetic pattern when the conveying magnetic pole 63 is provided between the dividing magnetic pole 61 and the developing magnetic pole 62 as in the present embodiment. FIG. 8A shows two developing rolls 42A and 42B. Are separated by a distance (corresponding to g0 in the figure) where the mutual magnetic action does not reach, and (b) shows a state of being placed close to each other (corresponding to g1 in the figure: g1 << g0).

  In (a), similarly to FIG. 7, the tangential component T1 of the magnetic flux density between the two due to the normal component R1 of the magnetic flux density due to the split magnetic pole 61 and the normal component R2 of the magnetic flux density due to the magnetic pole 63 for conveyance is The peak value appears at approximately the center of the two magnetic poles (the split magnetic pole 61 and the transport magnetic pole 63). However, when such developing rolls 42A and 42B are arranged close to each other, as shown in (b), the peak value of the normal component R1 ′ of the magnetic flux density of the split magnetic pole 61 is larger than that in (a). Since it greatly increases, the tangential component T1 ′ of the magnetic flux density between the split magnetic pole 61 and the transport magnetic pole 63 also changes compared to the case of (a). In this case, although the peak position of the tangential component T1 ′ slightly changes closer to the transporting magnetic pole 63, the transporting magnetic pole 63 is located near the dividing magnetic pole 61, and therefore there is no transporting magnetic pole 63 in FIG. It is different from the state of b). Further, although the peak value of the tangential component T1 ′ is slightly lower than that in FIG. 4A, the size of the portion (the portion indicated by Q in the figure) where the normal component R1 ′ of the split magnetic pole 61 starts to be small is It is secured to some extent. This indicates that a tangential component larger than the magnitude of the tangential component Ta ′ at the portion Q in FIG. 7B can be obtained. In (b), the Q portion on the developing roll 42B side is omitted.

  Thus, by providing the transport magnetic pole 63, a sufficient transport force is applied to the developer immediately after the division, and it is possible to suppress the separated developer from being peeled off from each of the developing rolls 42A and 42B. , A developer having a stable layer thickness is conveyed toward DB.

By the way, as in the comparative example shown in FIG. 9, the two developing rolls 201 and 202 are arranged to face each other, and the regulating member 203 is provided in the gap g ″ between the two developing rolls 201 and 202, and the developer G is placed on the two developing rolls 201 and 202. Here, (a) is a schematic diagram showing the flow of the developer G, and (b) shows a magnetic pattern.
This is because the developer G is supplied in a state of straddling the two developing rolls 201 and 202 on the upstream side of the regulating member 203, and the developer G is separated by a gap g ′ between the regulating member 203 and the developing rolls 201 and 202. The layer thickness is determined. The developing rolls 201 and 202 are provided with magnetic poles 204 and 205 having different polarities at positions facing the regulating member 203, and the developing roll 202 is provided with a magnetic pole 206 on the downstream side of the magnetic pole 205. Further, the gap in such a configuration includes a gap g ′ between the developing rolls 201 and 202 and the regulating member 203 and a gap g ″ between the developing rolls 201 and 202. These are the present embodiment (see FIG. 5). ) With g ′ <g1 << g ”.

  In this comparative form, the normal components Rc and Rd of the magnetic flux density of the two magnetic poles 204 and 205 arranged to face the regulating member 203 are not of such magnitude that the mutual magnetic poles 204 and 205 interact with each other. The magnetic action is merely caused by the gap g ′ with the regulating member 203. Therefore, the tangential component Td of the magnetic flux density between the magnetic pole 205 and the magnetic pole 206 (magnetic flux density normal component Re) in the developing roll 202 has a small peak value. In such an aspect, the developer G is retained on the upstream side of the regulating member 203, and therefore an excessive load acts on the developer G. Further, if the magnetic force of the two magnetic poles 204 and 205 facing the regulating member 203 is increased, the staying action of the developer G on the upstream side of the regulating member 203 becomes stronger, which is not preferable.

-Action when the magnetic pole for division is biased-
10A to 10C are explanatory views showing the influence on the developer G caused by the magnetic pole arrangement of the split magnetic pole 61, and FIG. 10A shows the first developing roll as in the present embodiment. 42A shows a state in which the dividing magnetic pole 61 of 42A is biased and arranged upstream of the dividing magnetic pole 61 of the second developing roll 42B, (b) shows a state in which the dividing magnetic pole 61 is arranged at the opposing position, and (c) shows A state is shown in which the split magnetic pole 61 of the first developing roll 42A is biased and arranged downstream of the split magnetic pole 61 of the second developing roll 42B.

  The flow of the developer G in such a state is estimated as follows. Here, it is assumed that the peak values of the normal components of the magnetic flux densities of the dividing magnetic pole 61 of the first developing roll 42A and the dividing magnetic pole 61 of the second developing roll 42B are substantially equal.

  In the magnetic pole arrangement as shown in (a), the developer G conveyed on the second developing roll 42B is first sucked by the dividing magnetic pole 61 of the first developing roll 42A, and a lot of the developer G is attracted to the first developing roll. A force f1 directed toward the 42A side acts. Thereafter, the developer G is substantially constrained by the attracting action f2 of the split magnetic pole 61 (N3 pole, S4 pole), and the developer rolls 42A and 42B are transported to both the developing rolls 42A and 42B by the conveying force. Developer G is separated. Therefore, it becomes easy to divide the developers G1 and G2 on the first developing roll 42A and the second developing roll 42B after the division into substantially equal parts. That is, the developer adhesion amount (MOS1) on the first developing roller 42A and the developer adhesion amount (MOS2) on the second developing roller 42B are obtained by moving the developer G at two locations by f1 and f2. Easily divided into equal parts (MOS1≈MOS2). Needless to say, if the peak values of the magnetic flux densities of the split magnetic poles 61 of the two developing rolls 42A and 42B are made different from each other, the substantially equal split ratio will be different. A large amount of developer G is divided on the side of the developing roll having a larger.

  In the magnetic pole arrangement as shown in (b), substantially the same magnetic force acts from both the first developing roll 42A and the second developing roll 42B by the two split magnetic poles 61, and the developer G rises. Since the developer G has been transported by the second developing roll 42B, the force f1 directed toward the first developing roll 42A acts strongly at the portion where the two split magnetic poles 61 are opposed. The developer G1 divided on 42A is likely to be larger than the developer G2 on the second developing roll 42B. That is, at the position where the two split magnetic poles 61 face each other, the developer adhesion amount of the first developing roll 42A by the force f1 that a part of the developer G on the second developing roll 42B moves toward the first developing roll 42A side. (MOS1) tends to increase as compared with the developer adhesion amount (MOS2) of the second developing roll 42B (MOS1> MOS2).

  Furthermore, in the magnetic pole arrangement as shown in (c), the developer G held and transported by the second developing roll 42B is continuously transported while being attracted by the split magnetic pole 61 of the second developing roll 42B. As the influence of the magnetic force of the split magnetic pole 61 of the first developing roll 42A increases, the developer G on the second developing roll 42B is attracted, and the force f1 directed toward the first developing roll 42A acts strongly, and the first Divided into developing rolls 42A. At this time, since most of the developer G on the second developing roll 42B is attracted by the split magnetic pole 61 of the first developing roll 42A, the developer G1 of the first developing roll 42A is more likely to be the first. It tends to increase compared to the developer G2 of the two developing rolls 42B. In other words, when the developer G is divided for the first time at the position where the dividing magnetic pole 61 of the first developing roll 42A acts, a force f1 of a part of the developer G toward the first developing roll 42A acts. The developer adhesion amount (MOS1) of one developing roll 42A tends to be larger (MOS1> MOS2) than the developer adhesion amount (MOS2) of the second developing roll 42B.

  In any state, since the conveying magnetic pole 63 is provided on the downstream side of the dividing magnetic pole 61, the separated developers G1 and G2 can be prevented from being separated from the developing rolls 42A and 42B. In this state, they are conveyed toward the development areas DA and DB.

  Further, in such a state, when the amount of the developer G supplied to the facing portion of the first developing roll 42A and the second developing roll 42B changes, that is, for example, when the image size is different, In the case where the amount of developer supplied is varied by changing the speed, it is estimated as follows. In (b) and (c), since the movement of the developer G is only one place (corresponding to f1), the amount of developer divided is easily different depending on the amount of developer supplied, and the division ratio is likely to change. In (a), since the developer G moves in two places, even when the amount of developer supplied is changed, a substantially equal division ratio is maintained. Therefore, in the present embodiment, the developers G1 and G2 divided by a substantially equal division ratio are conveyed toward the development areas DA and DB, respectively.

  In the present embodiment, the developer G1 on the first developing roll 42A among the developers divided in this way is subjected to development in the development area DA as shown in FIG. The developer G1 in the development area DA is more or less strongly applied to the photoconductor 21 because the first developing roll 42A rotates in a different direction at a portion facing the photoconductor 21. The magnetic carrier is prevented from being scattered to the photosensitive member 21 side.

  The developer G1 held by the first developing roll 42A and passing through the developing area DA is conveyed along with the rotation of the first developing roll 42A, and the first developing roll 42A is generated by a repulsive magnetic field between the S2 pole and the S3 pole. And is collected in the developer conveyance path 51 through the guide member 46 (see FIG. 4).

  On the other hand, the developer G2 on the divided second developing roll 42B is subjected to development in the development area DB as shown in FIG. The developer G2 in the development area DB is somewhat weakly applied to the photoconductor 21 because the second developing roll 42B rotates in the same direction at a portion facing the photoconductor 21. Therefore, the obtained toner image is not easily disturbed.

  The developer G2 held by the second developing roll 42B and having passed through the developing zone DB is conveyed along with the rotation of the second developing roll 42B, and is subjected to the second development by a repulsive magnetic field acting between the S2 pole and the S3 pole. It is peeled from the roll 42B and collected on the developer conveyance path 51 side (see FIG. 4).

  Then, as shown in FIG. 4, the developers G1 and G2 separated from the first developing roll 42A and the second developing roll 42B and collected in the developer conveying path 51 are developed by the agitating and conveying members 53 and 54 into two developments. By being agitated and conveyed while circulating in the agent conveying paths 51 and 52, the developer G having a desired charge amount and density is again used for development.

-Magnetic pole width of split magnetic pole and transfer magnetic pole-
Next, the magnetic pole widths of the dividing magnetic pole 61 and the conveying magnetic pole 63 will be described. FIG. 11 shows the magnetic pattern of the first developing roll 42A (R11 to R22 are the magnetic flux density) when the magnetic pole widths of the dividing magnetic pole 61 and the conveying magnetic pole 63 are different from each other (represented by half width here) at the same position. (A) shows a state in which the second developing roll 42B (not shown) is disposed so as to be opposed to the normal line component (a), and (a) shows that the half-value width θ21 of the conveying magnetic pole 63 is larger than the half-value width θ11 of the dividing magnetic pole 61. In the case (θ21> θ11), (b) is a case where the half-value width θ22 of the conveying magnetic pole 63 is smaller than the magnetic pole width θ12 of the dividing magnetic pole 61 (θ22 <θ12). An angle formed by a line segment connecting the central axis OA of the first developing roll 42A and the center position in the circumferential direction of the dividing magnetic pole 61 and a line segment connecting the center axis OA and the center position in the circumferential direction of the conveying magnetic pole 63. Is α + β (see FIG. 5).

The relationship between the developer flow and the half width (corresponding to the magnetic pole width) in such a magnetic pattern is estimated as follows.
In (a), since the half-value width θ21 of the conveying magnetic pole 63 is larger than the half-value width θ11 of the dividing magnetic pole 61, the tangential component T11 of the magnetic flux density between the dividing magnetic pole 61 and the conveying magnetic pole 63 is Even when the peak approaches the conveying magnetic pole 63 side, the size of the portion (the portion indicated by Q in the figure) where the normal component of the dividing magnetic pole 61 starts to be small is sufficiently secured. On the other hand, when the half-value width θ22 of the transport magnetic pole 63 is made smaller than the half-value width θ12 of the split magnetic pole 61 as shown in (b), the tangential component T12 of the magnetic flux density between the split magnetic pole 61 and the transport magnetic pole 63 is Since the peak is located on the conveying magnetic pole 63 side, the size of the portion (the portion indicated by Q in the figure) where the normal component of the dividing magnetic pole 61 has started to become smaller is smaller than that in (a).

  As a result, as shown in (a), when the half-value width of the conveying magnetic pole 63 is made larger than the half-value width of the dividing magnetic pole 61, a larger magnetic flux density is ensured immediately after the division. The peeling of the developer G is further suppressed. Even if it is like (b), it cannot be overemphasized that the magnetic flux density immediately after division | segmentation is ensured with sufficient magnitude | size compared with the case where the magnetic pole 63 for conveyance is not provided.

  Here, reference has been made to the half-value width of the conveying magnetic pole 63 and the dividing magnetic pole 61. Instead of the half-value width, for example, the occupation angle of the normal component of the magnetic flux density on the surface of the developing rolls 42A, 42B (corresponding to the zero point width) ), The length in the circumferential direction of the magnet forming the magnetic pole, the width of a predetermined ratio (for example, 80%) with respect to the peak value of the magnetic flux density, and the like.

-Layout of magnetic pole for conveyance-
Next, the layout of the conveying magnetic pole 63 with respect to the dividing magnetic pole 61 will be described. FIG. 12 shows a magnetic pattern on the first developing roll 42A side when the installation position of the conveying magnetic pole 63 is changed. Here, (a) assumes that the conveyance magnetic pole 63 is positioned approximately in the middle between the split magnetic pole 61 and the development magnetic pole (not shown), and (b) illustrates that the conveyance magnetic pole 63 is ( a) It is assumed that it is arranged slightly closer to the dividing magnetic pole 61.

  In this aspect, the half-value width θ1 of the split magnetic pole 61 and the half-value width θ2 of the transport magnetic pole 63 are set in substantially the same manner in (a) and (b). Is smaller than the half-value width θ2 of the conveying magnetic pole 63 (θ1 <θ2). In addition, an angle formed by a line segment connecting the central axis OA of the first developing roll 42 </ b> A and the circumferential center position of the dividing magnetic pole 61 and a line segment connecting the central axis OA and the circumferential center position of the conveying magnetic pole 63. (A) is γ1, and (b) is γ2 (γ1> γ2).

  In FIG. 12A, the magnetic flux density tangent between the split magnetic pole 61 and the transport magnetic pole 63 is caused by the normal component R13 of the magnetic flux density of the split magnetic pole 61 and the normal component R23 of the transport magnetic pole 63. Component T13 is produced. On the other hand, similarly in (b), the magnetic flux density between the split magnetic pole 61 and the transport magnetic pole 63 is determined by the normal component R14 of the magnetic flux density of the split magnetic pole 61 and the normal component R24 of the transport magnetic pole 63. The tangential component T14 is generated. In both the tangential components T13 and T14, the normal component of the split magnetic pole 61 starts to decrease as the tangential component peak value approaches the split magnetic pole 61 when the transport magnetic pole 63 is brought closer to the split magnetic pole 61. The size of the tangential component at the part (indicated by Q in the figure) increases. Therefore, the developer transportability is more stable in (b).

  Such an arrangement of the magnetic poles is expected to change depending on, for example, the size of the half width of the magnetic poles. However, when the two developing rolls 42A and 42B are arranged to face each other, the conveyance of the different polarities is performed. If the magnetic action between the magnetic poles 63 for use is within a range that does not affect each other, it is preferable to bring the conveying magnetic pole 63 closer to the dividing magnetic pole 61 side. As a result, the tangential component of the magnetic flux density between the split magnetic pole 61 and the transport magnetic pole 63 has a large rising slope from the split magnetic pole 61 side, and the tangential component increases in the vicinity of the split magnetic pole 61 accordingly. Become.

  However, if the transfer magnetic pole 63 is brought too close to the dividing magnetic pole 61, the interaction between the transfer magnetic poles 63 works, and the normal component of the magnetic flux density of the transfer magnetic pole 63 increases, so that the tangential component becomes smaller and the divided magnetic pole 63 becomes smaller. There is a possibility that the developer from the developing rolls 42A and 42B may be peeled off immediately. Further, if the transport magnetic pole 63 is too far from the split magnetic pole 61, the slope of the rising of the tangential component of the magnetic flux density from the split magnetic pole 61 tends to be gentle, and the normal component of the split magnetic pole 61 starts to decrease. The tangential component at the part becomes smaller. Therefore, it is better to bring the carrying magnetic pole 63 closer to the dividing magnetic pole 61 within a range where the magnetic action of the carrying magnetic poles 63 does not reach each other.

  In the present embodiment, the split magnetic pole 61 of the first developing roll 42A and the second developing roll 42B is biased to the upstream side. For example, the split magnetic pole 61 on the second developing roll 42B side is set to the downstream side. The split magnetic pole 61 of the first developing roll 42A may be biased upstream, and the split magnetic pole 61 of the second developing roll 42B may be biased downstream.

  Further, in the present embodiment, the split magnetic pole 61 of the first developing roll 42A is biased upstream from the split magnetic pole 61 of the second developing roll 42B. However, both split magnetic poles 61 are opposed to each other. Alternatively, the dividing magnetic pole 61 of the first developing roll 42A may be displaced downstream from the dividing magnetic pole 61 of the second developing roll 42B. In these arrangements, it is difficult to divide the division ratio equally, but it goes without saying that the conveyance of the developer after the division becomes stable by providing the magnetic pole 63 for conveyance.

  In the present embodiment, only the split magnetic pole 61 of the first developing roll 42A is biased to the upstream side. However, the conveying magnetic pole 63 of the first developing roll 42A is replaced with the conveying magnetic pole of the second developing roll 42A. 63 may be biased to the upstream side. If the splitting magnetic pole 61 and the transporting magnetic pole 63 are both biased, the developer G attracted to the first developing roll 42A side by the splitting magnetic pole 61 of the first developing roll 42A is transferred to the second developing roll 42B. Of the tangential components of the magnetic flux density between the split magnetic pole 61 and the transport magnetic pole 63 on the first developing roll 42A side, the split magnetic pole 61 method is used even when the split magnetic pole 61 is returned to the magnetic action. Since the size at the portion where the line component starts to decrease (for example, the portion Q in FIG. 8B) is sufficiently secured, the amount of the developer returned to the second developing roll 42B side is also reduced, which is substantially equally divided. It is easy to maintain the division ratio.

  In the present embodiment, the mode in which the photosensitive member 21 rotates in the downward direction in the figure at the portion facing the developing device 40 (clockwise rotation in the figure) is shown, but it rotates counterclockwise in the figure. It does not matter even if it does. In the present embodiment, both the first developing roll 42A and the second developing roll 42B are formed with a plurality of V-shaped grooves on the peripheral surface. For example, a U-shaped or trapezoidal groove shape may be applied, or a peripheral surface having a predetermined surface roughness may be obtained by performing a blasting process with a selected blast material.

Embodiment 2
FIG. 12 is a partially enlarged view of the developing device 40 according to the second embodiment, and is an explanatory view showing the movement of the developer G around the first developing roll 42A and the second developing roll 42B. The developing device 40 of the present embodiment is configured in substantially the same manner as in the first embodiment, but differs from the first embodiment in the number of magnetic poles of the first developing roll 42A and has a five-pole configuration. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

  In the present embodiment, the first developing roll 42A is disposed on the side near the developer transport path (not shown) obliquely above the second developing roll 42B. For this reason, the magnetic pole arrangement in the second developing roll 42B is configured in the same manner as in the first embodiment, but the magnetic pole arrangement in the first developing roll 42A is different from that in the first embodiment. The first developing roll 42A has five magnetic poles therein, the N2 pole corresponding to the position facing the second developing roll 42B is the dividing magnetic pole 61, and the S3 pole is the conveying magnetic pole 63. Further, the N1 pole corresponds to the developing magnetic pole 62, the S1 pole corresponds to the peeling magnetic pole, and the S2 pole corresponds to the magnetic pole that forms a repulsive magnetic field together with the S1 pole. Further, also in the present embodiment, as in the first embodiment, the split magnetic pole 61 (N2 pole) of the first developing roll 42A on the side where the developer G is not supplied is the split magnetic pole 61 of the second developing roll 42B. It is biased and arranged upstream from (S4 pole).

  In such a configuration, the developer G supplied to the second developing roll 42B side is a portion of the first developing roll 42A serving as the split magnetic pole 61 at a portion facing the first developing roll 42A and the second developing roll 42B. It is divided by the magnetic action of the N2 pole and the S4 pole of the second developing roll 42B. The divided developer G1 on the first developing roll 42A is conveyed by the S3 pole as the conveying magnetic pole 63 and reaches the developing area DA. The developer G1 developed in the development area DA is peeled from the first developing roll 42A by the repulsive magnetic field between the S1 pole and the S2 pole. The separated developer G1 is collected through a guide member 46 in a developer transport path (not shown).

  On the other hand, the divided developer G2 on the second developing roll 42B side is transported toward the development area DB by the S4 pole as the transport magnetic pole 63. The developer G2 developed in the development zone DB is peeled off from the second developing roll 42B by the repulsive magnetic field between the S2 pole and the S3 pole and collected in a developer transport path (not shown).

  Thus, in the present embodiment, since the first developing roll 42A is disposed obliquely above the second developing roll 42B, the peeling point for peeling the developer G1 from the first developing roll 42A is the split magnetic pole. This can be performed at a position far from the upstream side in the rotation direction of the first developing roll 42A from the portion where 61 (N2 pole) is arranged, and the number of magnetic poles can be reduced accordingly. The arrangement of the first developing roll 42A and the second developing roll 42B is not limited to this. For example, the first developing roll 42A and the second developing roll 42B may be arranged substantially horizontally. However, the number of magnetic poles of the first developing roll 42A can be reduced from seven.

Embodiment 3
FIG. 14 is a schematic diagram illustrating an outline of the developing device according to the third embodiment. In the developing device 40 of the present embodiment, the arrangement of the first developing roll 42A and the second developing roll 42B with respect to the photoreceptor 21 is substantially the same as that of the first embodiment, but the supply of the developer is the same as that of the first embodiment. Thus, the second developing roll 42B is not the first developing roll 42A disposed above but the second developing roll 42B. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

  In the developing device 40 of the present embodiment, a regulating member 45 that regulates the layer thickness of the developer G is provided on the first developing roll 42A side. Further, behind the first and second developing rolls 42A and 42B in the developing container 41, two developer conveying paths 51 and 52 arranged in the vertical direction in the figure are provided, and these developer conveying paths 51 are arranged. , 52 are provided with agitating and conveying members 53 and 54 for agitating and conveying the developer G, respectively. A passage through which the developer G can pass between the upper and lower developer transport paths 51 and 52 is formed at both ends in the longitudinal direction of the two developer transport paths 51 and 52. For example, the rotation of the lower stirring transport member 54 is rotated. Thus, the developer G in the lower developer transport path 52 can reach the upper developer transport path 51 side. Further, a magnetic permeability type density sensor 55 is attached to a lower oblique portion of the lower developer conveyance path 52 so that the toner concentration of the developer G in the lower developer conveyance path 52 is measured. It is configured. Reference numeral 46 denotes a guide member that guides the developer G peeled from the first developing roll 42 </ b> A to the developer transport path 51.

  FIG. 15 is a partially enlarged view of the developing device 40 of the present embodiment, and is an explanatory view showing the movement of the developer G around the first developing roll 42A and the second developing roll 42B. In the present embodiment, the magnetic pole arrangement is such that the split magnetic pole 61 (S4 pole) of the second developing roll 42B, which is the developing roll on the side different from the side to which the developer G is supplied, is supplied with the developer G. The first developing roll 42 </ b> A, which is the first developing roll, is biased upstream of the split magnetic pole 61 (N3 pole).

The operation of the developing device 40 having such a configuration will be described with reference to FIGS.
In the present embodiment, the developer G that has obtained a desired charge amount by being agitated by the two agitating / conveying members 53 and 54 causes the first developing roll 42 </ b> A to accompany the rotation of the upper agitating / conveying member 53. Is supplied toward the S2 pole. The layer thickness of the developer G supplied onto the first developing roll 42 </ b> A is regulated by the regulating member 45. The first developing roll 42A and the second developing roll 42B are opposed to each other by the magnetic action of the N3 pole of the first developing roll 42A as the split magnetic pole 61 and the S4 pole of the second developing roll 42B. The developer G held on the roll 42A is divided into a first developing roll 42A side and a second developing roll 42B side.

  Of the divided developers G1 and G2, the developer G1 on the first developing roll 42A side is conveyed toward the developing area DA by the S4 pole as the conveying magnetic pole 63. The developer G1 subjected to development in the development area DA is transported as the first developing roll 42A rotates, and is peeled off from the first developing roll 42A by the action of the repulsive magnetic field between the N2 pole and the N3 pole. The developer G1 peeled from the first developing roll 42A is collected to the developer transport path 51 via the guide member 46.

  On the other hand, among the divided developers G1 and G2, the developer G2 on the second developing roll 42B side is transported toward the development area DB by the N3 pole as the transport magnetic pole 63. The developer G2 subjected to development in the development area DB is transported with the rotation of the second development roll 42B, and is peeled off from the second development roll 42B by the action of the repulsive magnetic fields of the S2 and S3 poles. The developer G2 peeled off from the second developing roll 42B is collected as it is on the lower developer conveyance path 52 side.

  In particular, in the present embodiment, the split magnetic pole 61 of the second developing roll 42B that is the developing roll on the side to which the developer G is not supplied is the first developing that is the developing roll on the side to which the developer G is supplied. Since the rollers 42A are arranged to be deviated upstream from the dividing magnetic pole 61, the developers G1 and G2 supplied to the developing area DA and the developing area DB are substantially equally divided as in the first embodiment. It becomes easy to divide by the division ratio, and the developer G1, G2 after division is suppressed from variation in layer thickness, so that the uniformity of image quality can be improved. In the present embodiment, the photoconductor 21 may be rotated in the direction opposite to that shown in the figure (ie, it rotates counterclockwise in the figure).

Embodiment 4
FIG. 16 is a partially enlarged view of the developing device 40 according to the fourth embodiment, and is an explanatory view showing the movement of the developer G around the first developing roll 42A and the second developing roll 42B. The developing device 40 according to the present embodiment is configured in substantially the same manner as in the first embodiment, but the number of magnetic poles of the conveying magnetic pole 63 of the first developing roll 42A and the second developing roll 42B is different from that in the first embodiment, and each of them is different. It has two magnetic poles. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

  As the magnetic poles in the first developing roll 42A in the present embodiment, N1 pole, S1 pole, N2 pole, N3 pole, S2, N4 pole, and S3 pole are provided, and the N1 pole is the developing magnetic pole 62. The S2 pole is the split magnetic pole 61, and the N4 pole and the S3 pole are the transport magnetic pole 63. On the other hand, as the magnetic poles in the second developing roll 42B, there are provided S1, N1, N2, S2, N3, S3, and N4 poles. The S1 pole is the developing magnetic pole 62 and the N3 pole is for splitting. The magnetic pole 61, the S3 pole, and the N4 pole serve as the transfer magnetic pole 63. In this embodiment, the split magnetic pole 61 (S2 pole) of the first developing roll 42A that is the developing roll on the side to which the developer G is not supplied is the second developing that is the developing roll on the side to which the developer G is not supplied. The roll 42B is arranged so as to be biased upstream from the dividing magnetic pole 61 (N3 pole).

  In such a configuration, the developer G supplied to the second developing roll 42B side is a portion of the first developing roll 42A serving as the split magnetic pole 61 at a portion facing the first developing roll 42A and the second developing roll 42B. It is divided by the magnetic action of the S2 pole and the N3 pole of the second developing roll 42B. The divided developer G1 on the first developing roll 42A is transported by the N4 pole and the S3 pole as the transport magnetic pole 63 and reaches the development area DA. The developer G1 developed in the development area DA is peeled from the first developing roll 42A by the repulsive magnetic field between the N2 pole and the N3 pole. The separated developer G1 is collected through a guide member 46 in a developer transport path (not shown).

  On the other hand, the divided developer G2 on the second developing roll 42B side is transported toward the development area DB by the S3 pole and the N4 pole as the transport magnetic pole 63. The developer G2 developed in the development zone DB is peeled off from the second developing roll 42B by the repulsive magnetic field between the N1 pole and the N2 pole, and is collected in a developer transport path (not shown).

  In the present embodiment, the mode in which two magnetic poles are used as the transport magnetic pole 63 in both the first developing roll 42A and the second developing roll 42B has been described. However, the present invention is not limited to this. For example, for transporting one of the developing rolls The magnetic pole 63 may be a single magnetic pole, or three or more magnetic poles may be provided as the transporting magnetic pole 63. Further, when a plurality of magnetic poles are provided as the conveying magnetic pole 63, if the magnetic pole widths are made different, for example, if the magnetic pole width of the magnetic pole closer to the dividing magnetic pole 61 is increased, the tangential component of the divided magnetic flux density Is sufficiently secured.

  In the embodiment in which the two developing rolls 42A and 42B are arranged opposite to the photosensitive member 21, the angle from the split magnetic pole 61 to the developing magnetic pole 62, that is, in the circumferential direction of the split magnetic pole 61, is as follows. The line segment connecting the center position of the magnetic pole width along the rotation center of each developing roll 42A, 42B, and the center position of the magnetic pole width along the circumferential direction of the developing magnetic pole 62 and the rotation center of each developing roll 42A, 42B are connected. The angle formed with the line segment is generally less than 90 °. Therefore, a sufficient magnetic pole width can be obtained as the conveying magnetic pole 63, and in order to simplify the configuration, it is preferable to use one magnetic pole as the conveying magnetic pole 63.

Embodiment 5
FIG. 17 is a schematic diagram showing an outline of the developing device of the fifth embodiment. The developing device 40 of the present embodiment is characterized in that it includes three developing rolls 42 </ b> A to 42 </ b> C with respect to the photoreceptor 21. The arrangement of the first developing roll 42A and the second developing roll 42B is substantially the same as that of the first embodiment, but the third developing roll as an additional developing roll upstream of the first developing roll 42A in the rotation direction of the photoreceptor 21. The difference from the developing device 40 of the first embodiment is that 42C is provided. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

  In the developing device 40 of the present embodiment, the third developing roll 42C, the first developing roll 42A, the second developing roll 42B, and the three developing rolls are arranged side by side from the upstream side along the rotation direction of the photoconductor 21. Yes. The first developing roll 42A and the second developing roll 42B rotate in the same direction as in the first embodiment, and the third developing roll 42C rotates in the same direction as the first developing roll 42A. That is, at the portion facing the photoreceptor 21, the first developing roll 42 </ b> A and the third developing roll 42 </ b> C rotate in the opposite direction to the photoreceptor 21, and the second developing roll 42 </ b> B rotates in the same direction as the photoreceptor 21. In the present embodiment, the developer G1 on the first developing roll 42A is delivered to the third developing roll 42C side at a portion where the first developing roll 42A and the third developing roll 42C face each other. Yes.

  In the present embodiment, the regulating member 45 supported by the resin block 47c in the developing container 41 is disposed to face the second developing roll 42B. Further, behind the third developing roll 42C, a guide member 46 extending downward is supported by the resin block 47c. Needless to say, a developing bias is supplied between the three developing rolls 42A, 42B, 42C and the photosensitive member 21, respectively.

FIG. 18 shows an example of magnetic pole arrangement in the first developing roll 42A, the second developing roll 42B, and the third developing roll 42C in the present embodiment, and is an explanatory diagram showing the flow of the developer. Yes.
The first developing roll 42A is provided with an N1 pole as the developing magnetic pole 62, an S1 pole and an S2 pole for peeling the developer G1, an N2 pole as the dividing magnetic pole 61, and an S3 pole as the conveying magnetic pole 63. It has been. The third developing roll 42C includes an S3 pole for generating a repulsive magnetic field among the S1, N1, S2, and S2 poles as the developing magnetic pole 62, the S1 pole of the first developing roll 42A, and N2 poles and N3 poles provided corresponding to the S2 poles are provided. Also in the present embodiment, the split magnetic pole 61 (N2 pole) of the first developing roll 42A is upstream from the split magnetic pole 61 (S4 pole) of the second developing roll 42B in the rotation direction of the first developing roll 42A. It is biased to the side. The arrangement of the magnetic poles of the second developing roll 42B is omitted because it has the same configuration as in the first embodiment. In the present embodiment, the peripheral speed of the first developing roll 42A and the peripheral speed of the third developing roll 42C are substantially equal.

The operation of the developing device 40 having such a configuration will be described with reference to FIGS.
In the present embodiment, the developer G that has obtained a desired charge amount by being agitated by the two agitating / conveying members 53 and 54 causes the S3 of the second developing roll 42B to move along with the rotation of the agitating / conveying member 53. Supplied near the pole. The layer thickness of the developer G supplied onto the second developing roll 42B is regulated by the N2 pole as the regulating magnetic pole and the regulating member 45. The developer G of which the layer thickness is regulated is the N2 pole of the first developing roll 42A as the split magnetic pole 61 and the S4 of the second developing roll 42B at the facing portion between the first developing roll 42A and the second developing roll 42B. Due to the magnetic action of the poles, the developer G held on the second developing roll 42B is divided into the first developing roll 42A side and the second developing roll 42B side.

  Of the divided developers G1 and G2, the developer G1 on the first developing roll 42A is conveyed toward the developing area DA by the conveying magnetic pole 63 (S3 pole) while maintaining the division ratio. The developer G1 that has been developed in the development area DA is conveyed along with the rotation of the first developing roll 42A. The developer G1 conveyed on the first developing roll 42A is peeled off from the first developing roll 42A by the magnetic action of the S1 pole and S2 pole constituting the repulsive magnetic field. At this time, the third developing roll 42C is provided with the N3 pole and the N2 pole, which are different in polarity from the S1 pole and the S2 pole, corresponding to the S1 pole and the S2 pole of the first developing roll 42A. The developer G1 peeled from the developing roll 42A is transferred to the third developing roll 42C as it is. That is, in this embodiment, the magnetic action between the S1 pole and S2 pole provided on the first developing roll 42A and the N3 pole and N2 pole provided on the third developing roll 42C corresponds to the delivery section. . The delivery unit may be other than the method using the repulsive magnetic field described above, and a known method may be adopted.

  The developer G1 transferred to the third developing roll 42C is developed in the developing zone DC and further conveyed along with the rotation of the third developing roll 42C. Thereafter, it is peeled off from the third developing roll 42C by the magnetic action of the S2 pole and S3 pole constituting the repulsive magnetic field. The developer G1 peeled from the third developing roll 42C is collected to the developer transport path 51 side via the guide member 46.

  On the other hand, of the divided developers G1 and G2, the developer G2 on the second developing roll 42B side is transported toward the development area DB by the transport magnetic pole 63 (N3 pole). The developer G2 that has been developed in the development zone DB is transported with the rotation of the second developing roll 42B, and is peeled off from the second developing roll 42B by the magnetic action of the S2 pole and S3 pole constituting the repulsive magnetic field. The developer G2 peeled from the second developing roll 42B is collected on the developer transport path 51 side.

  As described above, in the present embodiment, with respect to the electrostatic latent image on the photosensitive member 21, the development area DC in the third development roll 42C, the development area DA in the first development roll 42A, and the second development roll 42B. Since development is repeated in the three development areas (DC, DA, DB in order) of the development area DB, the development efficiency for the electrostatic latent image on the photoreceptor 21 is improved as compared with the case where the third development roll 42C is not provided. To do. Further, the first developing roll 42A and the second developing roll 42B are each provided with a conveyance magnetic pole 63 (corresponding to the S3 pole of the first developing roll 42A and the N3 pole of the second developing roll 42B) after the division. Therefore, the developers G1 and G2 in which the variation in the layer thickness is suppressed are conveyed to each development area in a state where the division ratio is stable.

  In this embodiment, the rotating direction of the photoconductor 21 is rotated clockwise in the figure, but the photoconductor 21 may be rotated in the opposite direction (rotated counterclockwise in the figure). . In this case, in the drawing, the second developing roll 42B rotates in the opposite direction to the photoconductor 21 at the portion facing the photoconductor 21, and the first developing roll 42A and the third developing roll 42C are the portions facing the photoconductor 21. It rotates in the same direction as the photoconductor 21. Even if such a configuration is adopted, there are three development zones with the photoreceptor 21, and the development efficiency is improved as compared with the case where the third development roll 42C is not provided.

  Here, the third developing roll 42C is provided with respect to the first developing roll 42A. However, the third developing roll 42C may be provided on the second developing roll 42B side, or an additional developing roll may be provided. You may make it each provide in the one developing roll 42A and the 2nd developing roll 42B.

Example 1
In this embodiment, in order to confirm the usefulness of the magnetic pole for conveyance in the first developing roll 42A and the second developing roll 42B, a magnetic pattern having seven magnetic poles inside is shown. For comparison, a magnetic pattern in a five-pole configuration (first developing roll 42A ′, second developing roll 42B ′) that does not have a magnetic pole corresponding to the conveying magnetic pole is also shown.

  FIG. 19 shows a magnetic pattern in this embodiment, where the solid line is a normal component of magnetic flux density (corresponding to R1 to R7), and the dotted line is a tangential component of magnetic flux density (corresponding to T1 to T7). Here, the magnetic flux density of each of the two developing rolls 42A and 42B is 90 mT for the split magnetic pole (the magnetic pole corresponding to R1 in the figure) and 100 mT for the conveying magnetic pole (the magnetic pole corresponding to R2 in the figure). did. However, even if magnetic poles having such a magnetic flux density are arranged, they are arranged so as to face each other, so that the normal component of the magnetic flux density at the position of the observed magnetic pole for division (corresponding to R1 in the figure) is This is larger than the normal component (corresponding to R2 in the figure) of the magnetic flux density at the position of the conveying magnetic pole. Further, since the conveying magnetic pole is provided next to the dividing magnetic pole, a large value is secured for the tangential component T1 at the portion where the normal component of the magnetic flux density of the dividing magnetic pole falls. Needless to say, the normal component of the magnetic flux density of the developing magnetic pole (corresponding to R3 in the figure) is larger than the normal component of the magnetic flux density of the dividing magnetic poles arranged opposite to each other.

  On the other hand, FIG. 20 shows, as a comparative example, a magnetic pattern in the case where there are five magnetic poles that do not have a magnetic pole for conveyance. In this case, since the developing magnetic pole (magnetic pole corresponding to R2 in the figure) is arranged at a position adjacent to the downstream side of the dividing magnetic pole (magnetic pole corresponding to R1 in the figure), the magnetic flux density between them is The tangential component T1 is small in the vicinity of the dividing magnetic pole due to the influence of the dividing magnetic poles, and is inclined toward the developing magnetic pole. For this reason, the tangential component T1 at the portion where the normal component of the magnetic flux density of the dividing magnetic pole falls is very small and becomes large as it approaches the developing magnetic pole. Therefore, the divided developer is easily peeled off from the developing rolls 42A ′ and 42B ′.

  In this embodiment, by providing the transport magnetic pole between the split magnetic pole and the developing magnetic pole, the tangential component (corresponding to T1 in FIG. 18) of the magnetic flux density immediately after the split becomes a large value. Separation of the developer from the developing rolls 42A and 42B is suppressed, and stable conveyance is performed. As a result, the developer layer in which the variation in the division ratio is suppressed and the variation in the developer thickness is small is conveyed to the development area. On the other hand, in the comparative example, since the tangential component of the magnetic flux density immediately after the division is small, the developer immediately after the division is easily peeled off from the developing rolls 42A ′ and 42B ′, the division ratio is easily changed, and the thickness is also easily changed. The developer layer is conveyed to the development area.

  This is the same even when the dividing magnetic pole and the conveying magnetic pole of the developing roll on the side different from the developing roll to which the developer is supplied are arranged at the upstream side in the divided portion. Needless to say, the same applies even if the magnetic pole width of the conveying magnetic pole is made larger than the magnetic pole width of the dividing magnetic pole.

Example 2
In this example, as shown in FIG. 21, in the same manner as in the first embodiment, two developing rolls 101 and 102 are aligned in the vertical direction so as to be inclined by 7 ° from the vertical direction, and the lower developing roll is arranged. In the aspect in which the developer G is supplied to 102, when the angle of the upper developing roll 101 is changed, that is, the positional relationship between the split magnetic pole and the conveying magnetic pole in the upper and lower developing rolls 101 and 102 is changed. In some cases, it was confirmed what the developer split ratio would be. Here, the dividing magnetic poles are x1 and x2, and the conveying magnetic poles are y1 and y2. Reference numeral 100 denotes a photoconductor.

In such a configuration, the evaluation was performed under the following conditions.
・ Half width of split magnetic poles x1 and x2: constant (20 ° here)
-Magnetic flux density of magnetic poles x1 and x2 for splitting: 90 mT (single unit)
・ Half width of transfer magnetic poles y1 and y2: 2 levels of 30 ° and 20 ° ・ Magnetic flux density of transfer magnetic poles y1 and y2: 100 mT (single unit)
・ Developing roll peripheral speed v1, v2: v1≈v2
Further, the developer G is supplied from the lower developing roll 102 side, and the amount of developer supplied is set to two levels (low MOS, high MOS: Mass On Sleeve) by changing the gap with the regulating member. Further, the angle (referred to as upper MSA: MSA = Magroll Set Angle) was changed in the direction of rotation about the central axis O1 of the upper developing roll 101. At this time, in this embodiment, when the lower developing roll 102 is installed, the position of the split magnetic pole β2 of the lower developing roll 102 is the central axis O1 of the upper developing roll 101 and the central axis O2 of the lower developing roll 102. Although it was shifted 5 ° upstream from the line connecting the two, confirmation was performed in this state.

  The evaluation content is to determine the amount of each developer adhering (upper MOS, lower MOS) on the upper developing roll 101 and the lower developing roll 102 after the developer G is divided, and the ratio (upper MOS / lower MOS). MOS) was calculated. FIG. 21 shows the result when the half-value width of the magnetic poles y1 and y2 for conveyance under such conditions is 30 °, and FIG. 22 shows the result when the half-value width of the magnetic poles y1 and y2 for conveyance is 20 °.

From FIG. 21, the following points were confirmed.
Rotating the upper MSA toward the developer container (HSG), that is, biasing the magnetic poles x1 and y1 of the upper developing roll 101 to the upstream side makes it easier to set the developer split ratio to 1: 1.
-When the upper MSA is rotated toward the photosensitive member (PR), that is, when the magnetic poles x1 and y1 of the upper developing roll 101 are biased to the downstream side, a lot of developer is divided toward the upper developing roll 101. At the same time, when the rotation angle is slightly changed, the division ratio is changed.
-Even if the amount of developer supplied changes, the relationship between the upper MSA and the split ratio changes in substantially the same manner.
In order to make the split ratio approximately 1 to 1 even when the amount of developer supplied is changed, it is better to rotate the upper developing roll 101 by 2 to 6 degrees toward the developing container.

The following points were confirmed from FIG.
Rotating the upper MSA toward the developer container (HSG), that is, biasing the magnetic poles x1 and y1 of the upper developing roll 101 to the upstream side makes it easier to set the developer split ratio to 1: 1.
When the upper MSA is rotated toward the photoconductor (PR), that is, when the magnetic poles x1 and y1 of the upper developing roll 101 are biased to the downstream side, the upper half of the conveying magnetic pole is higher than when the half-value width is 30 °. A large amount of developer is divided toward the developing roll 101, and the dividing ratio is greatly changed by slightly changing the rotation angle.
When the amount of developer supplied is increased, the amount of increase in the developer on the upper developing roll 101 is less than when the amount is small.
In order to make the split ratio approximately 1 to 1 even when the amount of developer supplied is changed, it is better to rotate the upper developing roll 101 4 to 9 degrees toward the developing container.

  From the above, it has been understood that the division ratio can be stabilized when the half-value width (corresponding to the magnetic pole width) of the conveying magnetic pole is 30 ° rather than 20 °.

  Furthermore, the present inventor conducted the same evaluation as in this example with the two developing rolls having different peak values of the magnetic flux density of the splitting magnetic poles. It was confirmed that the developer was divided by the tendency.

  DESCRIPTION OF SYMBOLS 1 ... Image holding body, 2 ... 1st developer holding body, 3 ... 2nd developer holding body, 4 ... Developer supply mechanism, 5 ... Restriction member, 6 ... Developer division part, 7 (7a, 7b) ) ... dividing magnetic pole, 8 (8a, 8b) ... developing magnetic pole, 9 ... developer conveying section, 10 (10a, 10b) ... conveying magnetic pole, G ... developer, Da, Db ... developing area

Claims (8)

The electrostatic latent image is arranged opposite to the image holding member that holds the electrostatic latent image and circulates, rotates in the opposite direction to the image holding member, and develops the electrostatic latent image on the image holding member. A first developer holding body that holds and conveys a developer containing toner and a magnetic carrier toward the developed area;
The first developer holding member is disposed opposite to the image holding member and the first developer holding member on the downstream side in the moving direction of the image holding member, and is opposed to the first developer holding member. A second developer holding body that rotates in the same direction as the first developer holding body and holds and conveys the developer toward the developing area where the electrostatic latent image on the image holding body is developed. ,
Develop with respect to either one of the first and second developer holders at a position downstream of the development area in the rotation direction of the developer holder and upstream of the opposing portion of the two developer holders. A developer supply mechanism for supplying the agent;
A regulating member that regulates the developer supplied by the developer supply mechanism to a necessary amount to be developed by both the first and second developer holders;
Dividing magnetic poles having different polarities are arranged at opposing portions of the first and second developer holders, and a magnetic field for dividing formed by these dividing magnetic poles is supplied from the developer supply mechanism. A developer dividing section that divides the developer conveyed to the opposite part of one developer holding body into two developer holding bodies;
Among the first and second developer holders, a conveying magnetic pole having a different polarity from each other is arranged between the developing magnetic pole corresponding to each developing area and each of the dividing magnetic poles. Due to the magnetic flux density distribution of the magnetic pole for conveyance, the magnetic flux density of the portion adjacent to the developer dividing portion is increased as compared with the case where there is no magnetic pole for conveyance, and the divided developer is separated toward each development area. A developer transport section for holding and transporting;
A developing device comprising: The developing device according to claim 1,
The developer dividing portion includes a magnetic pole along the circumferential direction of the dividing magnetic pole of the developer holding body on the side different from the developer holding body to which the developer is supplied by the developer supply mechanism among the dividing magnetic poles. The rotation direction of the developer holder relative to the center position of the magnetic pole width along the circumferential direction of the dividing magnetic pole of the developer holder on the side where the developer is supplied by the developer supply mechanism A developing device characterized in that the developing device is set to a position biased upstream. The developing device according to claim 1 or 2,
When the half width of the normal component of the magnetic flux density due to the dividing magnetic pole of each developer holder is θ1, and the half width of the normal component of the magnetic flux density due to the transport magnetic pole is θ2, 2. A developing device according to claim 1, wherein both the dividing magnetic pole and the conveying magnetic pole are set so as to satisfy a relationship of θ1 <θ2. In the developing device according to any one of claims 1 to 3,
The developer conveying portion includes a magnetic pole along the circumferential direction of the conveying magnetic pole on the developer holding body side that is different from the developer holding body to which the developer is supplied by the developer supply mechanism among the conveying magnetic poles. The rotation direction of the developer holder relative to the center position of the magnetic pole width along the circumferential direction of the conveying magnetic pole of the developer holder on the side where the developer is supplied by the developer supply mechanism. A developing device characterized in that the developing device is set to a position biased upstream. In the developing device according to any one of claims 1 to 4,
At least the developer holder on the side to which the developer is supplied by the developer supply mechanism includes the developing magnetic pole, the dividing magnetic pole, and the transporting magnetic pole, and the developer holding body in the rotation direction of the developer holding body. A developing device comprising seven magnetic poles along the developing device. An image carrier that holds the electrostatic latent image and circulates;
The developing device according to any one of claims 1 to 5, wherein the developing device is provided to face the image carrier and develops the electrostatic latent image on the image carrier with a developer.
An image forming apparatus comprising: The image forming apparatus according to claim 6.
One or more provided separately from the first and second developer holders, arranged to face the image carrier and hold and transport the developer toward the development area facing the image carrier. Additional developer holder,
A delivery section for delivering the developer held and transported to the first and second developer holders to the additional developer holder;
An image forming apparatus comprising: The electrostatic latent image is arranged opposite to the image holding member that holds the electrostatic latent image and circulates, rotates in the opposite direction to the image holding member, and develops the electrostatic latent image on the image holding member. A first developer holding body that holds and conveys a developer containing toner and a magnetic carrier toward the developed area;
The first developer holding member is disposed opposite to the image holding member and the first developer holding member on the downstream side in the moving direction of the image holding member, and is opposed to the first developer holding member. A second developer holding body that rotates in the same direction as the first developer holding body and holds and conveys the developer toward the developing area where the electrostatic latent image on the image holding body is developed. ,
Develop with respect to either one of the first and second developer holders at a position downstream of the development area in the rotation direction of the developer holder and upstream of the opposing portion of the two developer holders. A developer supply mechanism for supplying the agent;
A regulating member that regulates the developer supplied by the developer supply mechanism to a necessary amount to be developed by both the first and second developer holders;
Dividing magnetic poles having different polarities are arranged at opposing portions of the first and second developer holders, and a magnetic field for dividing formed by these dividing magnetic poles is supplied from the developer supply mechanism. A developer dividing section that divides the developer conveyed to the opposite part of one developer holding body into two developer holding bodies;
Of the first and second developer holders, adjacent magnetic poles including the splitting magnetic pole and the developing magnetic pole between the developing magnetic pole corresponding to the respective developing areas and the splitting magnetic poles. One or more magnetic poles for conveyance are arranged so that the polarities are different from each other, and the magnetic flux density of the portion adjacent to the developer dividing portion is made larger than the case where there is no magnetic pole for conveyance by the magnetic flux density distribution of these magnetic poles for conveyance. A developer transport unit that increases and holds and transports the divided developer toward each development area in a separated state;
A developing device comprising:

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